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Math Help - Inverse of a Matrix: Solve for m, n, p

  1. #1
    Dug
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    Inverse of a Matrix: Solve for m, n, p

    m+2n+p=5
    3m+4n+p=8
    m-6n+2p=4

    There are 2 ways taught us to solve for this using matrix.
    The Inverse method and Row-Echelon method.
    In row echelon method i got this answer:

    m=1
    n=1/2
    p=3

    i know the answer is correct because when i substitute it to the equations above, i get the correct answer.

    (1)+2(1/2)+(3)=5
    3(1)+4(1/2)+(3)=8
    1-6(1/2)+2(3)=4

    My problem is, when I use the Inverse method, i get the determinant -18, and the rest of the process gives me a wrong answer.
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  2. #2
    Super Member Quacky's Avatar
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    I agree with your determinant. Can you post the rest of your working?
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  3. #3
    Dug
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  4. #4
    Super Member Quacky's Avatar
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    Quote Originally Posted by Dug View Post
    Looks to me like there are some substantial sign errors. I think you're trying to do too much at once.
    I think the matrix of cofactors should be:
    14 -5 -22
    -10 1 8
    -2 2 -2

    Edit: I've just made a correction.
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  5. #5
    Dug
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    Quote Originally Posted by Quacky View Post
    Looks to me like there are some substantial sign errors. I think you're trying to do too much at once.
    I think the matrix of cofactors should be:
    14 -5 -22
    -10 1 8
    -2 2 -2

    Edit: I've just made a correction.
    wow i feel stupid. thanks! i got the correct answer now
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